The present invention relates generally to methods for sampling liquids and, in particular, to a liquid sampling system that minimizes sample cross-contamination and is also portable and adaptable for use in extreme climatic conditions and challenging physical environments. The invention is particularly advantageous for use in the field, where the user desires to collect multiple samples in succession, without contamination of latter samples by previous ones. The invention provides advantages in collecting samples from sites located underground or in difficult terrain, or where the user desires to avoid contact with the sample liquid. Because the invention uses a vacuum pump to draw samples, it also is advantageous where the user desires to collect large field samples, in excess of 500 milliliters in volume.
A variety of liquid sampling devices and methods have been developed for use in the laboratory and field. Only a few of these have been designed specifically to address the problem of sample contamination. A common contamination problem is cross-contamination of samples. This occurs when a sample device""s collecting tube or vessel is used repeatedly, without cleansing, to collect multiple samples. Each of the samples taken may leave liquid droplets or residue on the walls of the sample collecting tube or vessel. The latter samples taken are then contaminated by droplets or residue left in the tube and vessel by previous samples. This problem can be especially challenging in the field, where there usually is no access to washing facilities and autoclaves, as there might be in the laboratory. Field methods of flushing or purging the intake tube or receptacle with distilled water or other solvents, or with a burst of air or inert gas, often do not completely remove droplets or residue that may adhere to the walls of the collecting tube or vessel and contaminate later samples. Such droplets and residue can introduce substantial error in sampling results, especially when samples are collected for microbial analysis or analysis of relatively low levels of chemical pollutants. Field devices that are designed to address the issue of sample contamination, such as the cup and rod, grab bag, ampule, and cylinder samplers, can be awkward to use in challenging environments. Each of these requires the user to lift or pull the sampling device, containing the collected sample, out of the sample site to the user""s work area. The cup and rod sampler, for example, consists of a long rod to which is attached a cup for collecting samples. The user must grasp the rod by its handle and dip the cup into the body of liquid to be sampled. Once he has collected a sample in the cup, he must lift the cup out of the sample site and pivot it around to his work are With a cylinder sampler, the user lowers a cylindrical sampling device into the body of liquid to be sampled by means of a cord or cable attached to the sampling device. Once the sample is captured, the user raises the cylinder to the surface by pulling the cord or cable. With these types of sample devices, the user generally supplies the power for collecting the sample, and the size of the sample collected can be limited by the strength and stamina of the user. In addition, because of their shape and size, these devices are often difficult to use with certain sample souses, such as underground aquifers, storage tanks, ponds and streams in winter conditions (wholly or partially covered by ice), hot springs, septic and waste water tanks and lagoons and the lower strata of large bodies of water. Moreover, the method for avoiding sample contamination usually requires the user manually to remove a sample receptacle from a sampling device covered with the liquid sampled, exposing the user to contact with the liquid sampled. This can be awkward in the best of conditions, and especially in sub-freezing conditions or where the sample site is extremely hot, but also can be unpleasant and create a health risk for the user when the liquid sampled contains toxic chemicals or bacteria.
The present invention provides a system for collecting liquid samples in the field, using a vacuum pump to draw the liquid from the sample site through a hollow sample intake tube to the sample receptacle. An important feature of the invention is the independence of the vacuum pump system and the sample intake tubing. This is accomplished by use of a vacuum chamber with separate entry ports for these two functions, one entry port furnishing a connection to the vacuum pump system and the other providing access to the sample intake tubing. Once the sample intake tubing is inserted into the chamber, the intake tubing is then further inserted into an open sample receptacle placed within the chamber. When the chamber is closed and the vacuum pump engaged, air is drawn out of the vacuum chamber and the open sample receptacle within it, creating a partial vacuum that also draws liquid sample through the sample intake tube and into the sample receptacle. The chamber is preferably either made of transparent material or has a window which permits observation of the level of liquid in the sample receptacle. Once the desired quantity of liquid is collected in the sample receptacle, the vacuum pump is disengaged, and the chamber may be opened to allow removal of the sample receptacle for storage and transport to the laboratory, and placement of a new sample receptacle in the chamber. Also, the sample intake tubing can be removed and replaced with a new piece of intake tubing, so preventing contamination of the next sample by the one just taken. Used sample intake tubing can either be disposed, or saved and returned to the laboratory for cleansing. It is to be appreciated that this method avoids filling the vacuum chamber with, or immersing the sample receptacle in, sample liquid, so that the user can remove, replace and store sample receptacles without coming into contact with the sample liquid.
The use of hollow tubing, of whatever length and diameter desired to draw the sample, and vacuum power to transport the sample liquid to the sample receptacle, makes the invention highly versatile in the field. The intake tubing, particularly if fitted with rigid tubing on the sample collection end, can be inserted or directed through narrow openings in ice, vegetation, soil, or rock layers to gain access to liquid sample sites under frozen ponds or streams, in bogs or marshes, or underground. Hollow tubing also is very adaptable to insertion in narrow access pipes or tubes to storage tanks, and septic and sewage systems. It can be cut in long lengths and weighted and tossed across or into hot springs and geyser pools, fast running streams, and open sewage and wastewater lagoons. It can be attached to a rod or dowel to facilitate precise placement of the sample collection end into a particular area of a body of sample liquid. Further, the use of a vacuum pump system provides the power to draw the liquid sample up from a sample site located at an elevation much lower than the sample receptacle. The vacuum pump system also provides the capacity to draw numerous samples in succession, or a single large sample.
Because the vacuum chamber and vacuum pump system do not come in contact with the liquid sample, they may be constructed of lightweight materials such as plastic. Moreover, the vacuum pump system can be powered either manually by a hand pump, such as those readily available in the market, or by a small battery, such as a 12 volt battery used in motorcycles. These features of the system and use of lightweight hollow tubing for collecting samples make the invention, in many of its applications, highly portable, which enhances its advantage when used in field work, especially on ecological projects in wilderness and other difficult terrain.
The invention thus provides a system for obtaining liquid samples without cross-contamination of samples, and enhances the user""s capacity to collect samples of various sizes in challenging physical environments with reduced physical effort and lowered risk that the sample liquid will contact the user""s skin or clothing.